There has been increasing interest in the role of genetic influences on behavior and cognition in the last decade. Studies of such genetic conditions provide us with a unique opportunity to study gene-behavior and brain-behavior relationships in a genetically well-defined population. Nephropathic cystinosis is a genetic disorder in which a specific cognitive profile of visual spatial dysfunction, with spared visual perceptual function, intelligence, and language, has been documented. Brain MRI scans and neuropathological data have suggested a possible defect in myelination of the white matter. The mechanisms underlying these problems, and the course of the dysfunction over time are not known. The proposed study will use a longitudinal approach to study visual perceptual and visual spatial function over time in children and adolescents with cystinosis as well as controls; to perform serial MR/scans on children and adolescents with cystinosis; and to conduct morphometric analyses of the MRI scans to identify regional structural differences between cystinosis and control brains, in particular in the white matter. The study will take advantage of the already existent large database of cognitive studies in the cystinosis population obtained by this laboratory, so that subjects previously tested will undergo repeat testing to provide longitudinal information about changes in cognitive function and brain structure as the child gets older. The results of this study provide the potential for understanding the role of early metabolic and genetic dysfunction on subsequent brain development, both structural and functional, and for determining whether the presence of the metabolic disorder can produce a progressive deleterious effect on brain function. The study results may also provide a basis for developing early interventions for children "at risk" for cognitive deficits because of the presence of a genetic disorder.